Cable tension indicator device



Nov. 12, 1968 .I. M. LOWE CABLE TENSION INDICATOR DEVICE 2 Sheets-Sheet 1 Filed May 5, 1966 INVENTOR. a/mes M [OM/Q 01 .LQAJ

ATTORNEYS Nov. 12, 1968 LOWE CABLE TENSION INDICATOR DEVICE 2 Sheets-Sheet 2 Filed May 5, 1966 IN VEN TOR. James flZon e ATTORNEY? United States Patent 3,410,246 CABLE TENSION INDICATOR DEVICE James M. Lowe, 7647 MacArthur Blvd, Cabin John, Md. 20731 Filed May 5, 1966, Ser. No. 547,927 8 Claims. (Cl. 116-114) ABSTRACT OF THE DISCLOSURE In material hoisting apparatus of the type employing a boom on which a load handling cable is reeved, it is realized by those skilled in the art that the maximum load which can be lifted varies, depending upon the attitude of the boom; thus,"the maximum load Which can be lifted when the boom is in a horizontal position is somewhat less than that which can be lifted when the boom is in a substantially vertical position. Furthermore, in cranes employing extensible booms, the maximum load which can be lifted also depends upon the moment arm determined by the distance which the boom is extended and the capacity of the load being lifted at the end of the boom. Thus, a crane is capable of lifting a heavier load when the boom is in the retracted position than when the boom is in an extended position. Therefore, the range between minimum and maximum load limits is a function of the booms attitude which includes the position of the boom in the vertical plane and the length to which the boom is extended. Hence, in order that the boom will not become damaged, it is important that the crane operator does not lift a greater load than that which can be safely lifted, while the boom is positioned in a particular attitude.

Various types of tension indicators have been proposed to Warn the crane operator of the amount of tension being placed on a load cable to prevent damage to the crane boom. In one proposed arrangement, the indicator includes a fluid-actuated gage for indicating the tension on the cable, and in another proposed arrangement, the tension indicator is operatively connected to the controls of the cable winch, whereby the winch is automatically stopped when an excessive load is placed on the cable.

While these hitherto-employed tension indicators have been satisfactory for their intended purpose, they have been open to certain objections due to their complicated design and their inaccuracy of indicating the exact moment at which the load limit has been reached.

After considerable research and experimentation, the cable tension sentinel of the present invention has been devised to overcome the disadvantages experienced in hitherto-employed tension indicators and comprises, essentially, a pair of oppositely extending arms pivotally connected together at their adjacent ends. A pair of spaced, parallel plate members are integrally connected to the ends of the arms adjacent the pivotal connection, and a spacer plate having an arcuate peripheral edge is positioned Within the space between the plate members and integrally secured to the inside face of one of the plate members. A plurality of apertures extend through the plate members and spacer plate, each aperture being adapted to receive a selected shear pin for maintaining the arms in an oppositely extending relationship, and

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spring means are provided for holding the selected shear pin in its respective aperture. The outer end of each arm is provided with a disc rigidly connected thereto, said disc having a U-clamp associated therewith for guiding the load cable on the disc.

In use, the sentinel is placed on the lifting cable of a crane assembly by reeving the cable under the peripheral edge of each of the discs on the outer ends of the arms and passing the cable over the peripheral edge of the spacer plate. By this construction and arrangement, a loop is formed in the cable, which tends to straighten out due to the tension imparted to the cable when a load is being lifted. If the load being lifted is of a greater magnitude than that which can be supported by the selected shear pin, the pin will break allowing the cable to straighten out causing the arms to pivot out of the oppositely extending relationship, to thereby warn the crane operator to cease lifting the load whereby damage to the crane boom is prevented.

An object of the invention is to provide an improved cable tension sentinel.

Another object of the invention is to provide an improved cable tension sentinel having a pair of oppositely extending arms pivotally connected at their adjacent ends and maintained in an oppositely extending relationship by shear pin means adapted to fracture when a predetermined excessive load is placed on the cable thereby allowing the arms to pivot out of alignment to thereby Warn the crane operator to cease lifting the load to pre vent damage to the crane boom.

Still another object of the invention is to provide an improved cable tension sentinel having a shear pin adapted to fracture when a predetermined excessive load is placed on the cable thereby actuating the sentinel, whereby the crane operator is alerted to cease lifting the load to prevent damage to the crane boom, the sentinel being constructed and arranged to receive a selected one of a plurality of shear pins, each having a different shear strength.

Yet another object of the invention is to provide an improved cable tension sentinel characterized by its simplicity and ruggedness of construction, having relatively few moving parts and which is not likely to get out 0 order even after long and continued use.

With these and other objects in view, which may be incident to my improvements, the invention consists in the parts and combinations to be hereinafter set forth and claimed with the understanding that the several necessary elements, comprising my invention, may be varied in construction, proportions and arrangement, without departing from the spirit and scope of the appended claims.

In order to make my invention more clearly understood, I have shown in the accompanying drawings means for carrying the same into practical effect, without limiting the improvements in their useful applications to the particular construction which, for the purpose of explanation, have been made the subject of illustration.

In the drawings: v

FIGURE 1 is an elevational view showing the cable tension sentinel of the present invention mounted on the load line of a crane;

FIGURE 2 is a side elevational view of the sentinel mounted in operative position on a cable;

FIGURE 3 is a side elevational view showing the sentinel after a shear pin has fractured;

FIGURE 4 is a view taken along line 44 of FIG- URE 2;

FIGURE 5 is a view taken along line 55 of FIG- URE 4;

FIGURE 6 is a view taken along line 66 of FIGURE 4; and

FIGURE 7 is an exploded view showing the various components of the sentinel.

Referring to the drawings and more particularly to FIGURE 1, the cable tension sentinel 1 is adapted to be mounted on the load cable 2 of a conventional mobile crane assembly 3 having a boom 4 on which the load cable is reeved. The crane assembly is provided with suitable controls (not shown) for sluing the boom in a horizontal plane about a vertical axis 5 and for pivoting the boom in a vertical plane about a horizontal axis 6, the various positions of the boom in the vertical plane being shown in phantom at 4a, 4b and 4c. The maximum load which can be lifted by the cable without damaging the boom will vary, depending upon the attitude of the boom. The attitude of the boom not only includes the position of the boom in the vertical plane, but also, in the case of extensible booms, the length to which the boom is extended; thus, the heaviest load can be lifted by the crane when the boom is in the elevated, retracted position indicated at 40, the magnitude of the load capable of being lifted decreasing proportionately until the boom assumes the horizontal position as shown in full lines in FIGURE 1, the lifting capacity being further diminished if the boom were extended.

To lift a load of a known magnitude presents no problem to a crane operator since the boom can be first pivoted to its proper position in the vertical plane and the load can then he hoisted by the cable 2. However, when a load of unknown magnitude is to be lifted, the crane operator, assuming he does not have the benefit of the sentinel of the present invention, has to use his own judgment as to Which position the boom should be pivoted prior to lifting the load. Even if he places the boom in position 40, the position at which the greatest load can be lifted, he is still not sure whether the load of unknown magnitude can be lifted without damaging the boom.

In order to relieve the crane operator from the problem of surmising at which position the boom should be pivoted and to prevent possible costly damage to the boom, the sentinel of the present invention has been devised and comprises, as will be seen in FIGURES 2 and 7, a pair of oppositely extending arms 7 and 8 having their adjacent end portions disposed in overlapping relationship, arcuately-shaped plate extensions 7a and 8a being formed on the overlapped end portions of each of the respective arms. A spacer plate 9 having an arcuate peripheral edge 9a is positioned between extension plates 7a and 8a and integrally secured to the inside face of extension plate 8a.

As will be seen in FIGURE 5, the perihperal edge of the spacer plate is formed with a groove 9b to accommodate the load a cable 2 and to form a cable offsetting means when the sentinel is mounted thereon, to be described more fully hereinafter. It will also be noted that the radius of spacer plate 9 is less than the radius of each of the plate extensions 7a and 8a, whereby the upper edge portions of plate extensions 7a and 8a form spaced Walls for guiding the lateral surfaces of the cable. The arms 7 and 8 are freely pivoted to each other at their adjacent ends by means of a bolt 10 extending through aligned apertures 7b, 8b and 9c formed in the arms 7, 8 and spacer plate 9, respectively, the bolt being held therein :by suitable lock nuts 11.

Arms 7 and 3 are maintained in oppositely extending relationship by means of a shear pin 12 extending through selected, aligned apertures 13 formed in the plate extensions 7a, 8a and spacer plate 9, additional apertures 14 and 15, of different diameters, also being formed in the plate extensions and spacer plate for accommodating other shear pins having selected shear strengths. As will be seen in FIGURES 2 and 4, the shear pin apertures are arranged in the extensions and spacer plate in such a manner that only one shear pin can be employed at any given time; thus, when apertures 13 are aligned to receive a shear pin, apertures 14 and 15 in extension 7a will be misaligned with respect to the corresponding apertures in spacer plate 9 and associated plate extension 8a; accordingly, when either apertures 14- or 15 are aligned to receive a respective shear pin, the remaining apertures will be misaligned.

A pair of leaf springs 16 are pivotally mounted as at 17 to the outer faces of plate extensions 7a and 8a for maintaining the selected shear pin within the respective apertures to thereby prevent fractured pieces of the pin from being propelled outwardly from the sentinel in the event that the shear pin should break, to be described more fully, hereinafter. As will be seen in FIGURE 2, the leaf springs are of suflicient length whereby they may be pivoted to difierent positions to hold the selected shear pin in its respective aperture.

The outer end portions of each of the arms is provided with a disc 18 rigidly connected to the inner surface of the respective arm, each disc being provided with a groove 18a on its peripheral edge to accommodate load cable 2. A U-clamp 19 is pivotally connected to each disc by means of a wing-bolt 20 extending through aligned apertures 19a, 19b, 18b and formed in the arms of the U-clamp, the disc and the sentinel arm, respectively; the end of the bolt being threaded into a nut 21 secured to one of the arms of the U-bolt in alignment with aperture 19b formed therein.

When mounting the sentinel 1 on the load cable 2, the U-clamps 20 are first removed from each of the discs 18 and the cable is slipped over the grooved peripheral edge 9b of the spacer plate 9, and under the peripheral edge of each of the discs 18, as shown in FIGURE 2. The U-clamps are then secured to the discs to thereby form guides for the cable on the discs. The arms 7 and 8 are then slightly pivoted in order to align either shear pin apertures 13, 14 or 15 for accommodating a selected shear pin for holding the arms 7 and 8 in oppositely extending relationship, the selected shear pin being held within its respective aperture by means of the leaf springs 16 engaging the ends of the shear pin.

By the construction and arrangement of the sentinel mounted on the cable, a loop is formed therein which tends to straighten out when tension is applied thereto; thus, a force is created acting in a direction from the bight portion of the loop toward the shear pin, and a reaction force is created on each end of the arms acting in the opposite direction tending to pivot th arms about bolt 10. When the force exceeds the design limit of the selected shear pin, the pin breaks, allowing the cable to straighten out which causes the arms 7 and 8 to pivot to a position as shown in FIGURE 3 to thereby warn the crane operator to cease lifting the load.

As will be seen in FIGURE 1, the cable tension sentinel 1 is mounted on the load cable in the vicinity of the load to be lifted so that if the shear pin should break, the sentinel will only slide a short distance on the straightened cable, and when the sentinel is being employed on a crane having an extensible boom, as shown in FIGURE 1, a small capacity shear pin, for instance 2500 p.s.i., would be used when boom 4 is positioned in an extended horizontal position, and the largest capacity pin, for instance 6000 psi, would be used when the boom is positioned in the retracted, vertical position 4c.

The shear capacity of the pins may be designated on the faces of the arm plate extensions 7a and 8a, and, while for purposes of illustration, the sentinel of the present invention is adapted to selectively accommodate shear pins of three different capacities, it will be appreciated by those skilled in the art that the sentinel may be designed to accommodate a myriad of selected shear pins, provided that the shear pin apertures are formed in such a manner that only one shear pin may be inserted into the sentinel to hold the arms 7 and 8 in oppositely extending relationship.

From the above description, it will be readily apparent that the cable tension sentinel of the present invention provides a relatively simple and inexpensive device for Warning the crane operator that the load being lifted is too heavy for the boom, and the breaking of a relatively inexpensive shear pin to actuate the device prevents the warping and ultimate damage to the crane boom which is quite costly to repair not only in money but in lost manhours.

While I have shown and described the preferred embodiment of my invention, I wish it to be understood that I do not confine myself to the precise details of construction herein set forth by way of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, without departing from the spirit of the invention or exceeding the scope of the appended claims.

I claim:

1. A cable tension indicator device of the character described comprising, a pair of arms adapted to be mounted on a cable, pivot means connecting adjacent ends of said arms to each other, shear pin means coupling said pair of arms for holding the arms in a first position with respect to each other when mounted on a cable, cable guide means mounted on the distal ends of said arms, and cable ofisetting means connected to at least one of said arms intermediate the ends thereof, whereby when the device is mounted in operative position on a cable, the cable guide means engages one side of the cable, and the cable offsetting means engages the opposite side of the cable to thereby form a loop in said cable, whereby when a tension force above a predetermined value is applied to the cable urging the loop portion of the cable to straighten out, said shear pin means fractures allowing the arms to pivot into a second position with respect to each other.

2. A cable tension indicator device according to claim 1 wherein the cable offsetting means comprises an arcuate plate secured to one of said arms in proximity to the pivotal connection, and the cable guide means comprises a disc connected to the free end of each of said arms, the radius of said plate being greater than the radii of said discs, whereby when the sentinel is mounted in operative position on a cable, the peripheral edge of said plate engages one side of the cable and the peripheral edges of the discs engage the opposite side of the cable to thereby form the loop in said cable.

3. A cable tension indicator device according to claim 1, wherein said shear pin means comprises aperture means formed in said arms, and a shear pin mounted in said aperture means and extending between said pair of arms for holding said arms in said first position.

4. A cable tension indicator device according to claim 3, wherein said aperture means comprises a plurality of openings formed in one of said arms, each of said openings being alignable with a corresponding opening formed in the other of said arms, each of the aligned openings being adapted to receive a respective pin having a predetermined shear strength, the openings being arranged in each of the arms so that only one pair of openings can be aligned at any one time for receiving a selected shear pin, whereby only one selected shear pin can be employed for holding the arms in said first position.

5. A cable tension indicator device according to claim 3, wherein means are connected to the arms for holding the shear pin in operative position within said aperture means.

6. A cable tension indicator device according to claim 5, wherein the means for holding the shear pin in operative position comprises a pair of leaf springs, one end of each leaf spring being connected to a respective arm and the other end of each leaf spring engaging a respective end of the shear pin.

7. A cable tension indicator device according to claim 2, wherein a plate extension is connected to each arm at their adjacent ends, the arcuate plate being disposed between said plate extensions, the peripheral edge of the arcuate plate being disposed in a plane lower than the upper edges of the plate extensions, whereby the plate extensions form spaced walls for guiding the cable on the peripheral edge of the arcuate plate.

8. A cable tension indicator device according to claim 2, wherein U-clamp means are connected to each of said disc means for guiding the cable on the peripheral edges of said disc means.

References Cited UNITED STATES PATENTS LOUIS \J. CAPOZI, Primary Examiner. 

